This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 102 04 248.9, filed on Feb. 2, 2002, the entire disclosure of which is incorporated herein by reference.
The invention relates to a filter arrangement for a vacuum toilet system including at least one filter element for removing liquid and solid contaminants from a volume flow of air, whereby the filter element is arranged in a filter housing that is connected to the top of the waste water tank of the vacuum toilet system.
Commercial aircraft for passenger transport are typically equipped with a vacuum toilet system, which includes a waste water tank and at least one toilet and/or other waste disposal receptacles connected to the waste water tank by a waste collection line, and which uses a vacuum suction effect to suck the waste materials that are to be conveyed from the toilet into the waste water tank. This waste material stream or flow is a mixture of cabin air and waste water that comprises the toilet flush water, liquid and solid human waste, and other materials such as toilet paper, tissues, and other wastes that a passenger might dispose of into the toilet. The suction effect is typically created by the pressure difference between the low outside ambient air pressure and the higher interior pressure within the aircraft cabin during flight at typical cruise altitudes. Another possibility for generating the vacuum or suction effect is through the use of a conventional vacuum generator, for example when the aircraft is on the ground or at a low flight altitude which would provide an inadequate pressure differential.
The vacuum toilet system is connected via the waste water tank and through an outlet or exhaust air line to the external environment outside the aircraft. In other words, the outlet or exhaust line is connected from the waste water tank, for example through the vacuum generator or the like, to an overboard exhaust air outlet. The flow of cabin air and waste water is conveyed from the toilets through the collection line into the waste water tank, where the waste water is collected in the tank by the effect of gravity, while the airflow is conveyed out of the tank through the exhaust airline. However, this airflow leaving the waste water tank can still be contaminated with some liquid and solid wastes, for example due to the vigorous intermingling of the air with the solid and liquid wastes during the vacuum transport through the waste collection line. In order to separate and isolate the waste-contaminated portion of the toilet system from the outside exhaust air, and from the devices needed for generating the vacuum pressure differential, it is therefore necessary to provide a filter system for the exhaust air as it leaves the tank.
At present, the conventional filter systems installed in aircraft toilet systems are all embodied as volume, bulk, or storage filters. In other words, the present conventional filter systems all achieve the required filtration in the body volume or bulk of a filter medium. A conventional so-called waste separator comprising such a filter is typically arranged between the waste water tank and the exhaust air line. The contaminated airflow exiting from the waste water tank or the waste collection line is filtered and thereby decontaminated through the waste separator, and the output filtered airflow is then directed through the exhaust air line to the outside environment. Thereby, it is intended that any remaining solid or liquid waste contaminants are filtered out and removed from the airflow by the waste separator.
In the typical conventional arrangement of such a waste separator 100, e.g. as shown in present FIG. 1, a first filter element 102 consisting of a crimped or random-looped Perlon thread is arranged in a housing 101 including a bottom baffle 101A. This first filter element 102 separates any remaining contaminants, and especially liquid contaminant residues, from the unfiltered contaminant-laden airflow 2, which flows around and then up over the baffle 101A and into the bottom of the filter 102. The separated liquid runs down by the effect of gravity and drains through a small opening 103 in the bottom of the housing 101, i.e. in the bottom of the baffle 101A, back into the waste water tank. Since the conveyed airflow 2 can also be contaminated with small solid contaminant particles of toilet paper, tissues, newspaper, other waste paper, or other similar solid waste materials, such solid particles can be sucked against the bottom inlet surface of the filter element 102, or can be sucked into the bulk volume of the filter element 102, or can become lodged and thus plugged-up in the drain opening 103 of the housing 101.
The conventional arrangement of the waste separator 100 further includes a second filter element 104, consisting of a wound or rolled steel wire braid or mesh, arranged above the first filter element 102. After emerging from the top of the first filter 102, the partially filtered airflow is directed radially outwardly by another baffle 101B and then passes upwardly through the second filter element 104, where it is further cleaned or separated from contaminants. The final resulting filtered airflow 3 is then directed out of the exhaust air line 105.
The conventional filter system described above suffers the substantial disadvantage that it can become clogged, plugged or saturated with waste materials, and especially solid particle waste materials. Namely, as described above, solid waste materials such as paper particles and the like can become sucked onto the surface or into the body or volume of the crimped or crinkled fiber material of the first filter. Over time, the solid waste particles accumulate on the surface and in the body of the filter and begin to plug it up. Any solid waste particles that manage to get through the first filter can then become adhered on and plug the second filter consisting of a steel wire mesh or braid. This plugging of the filter system, which worsens over time, progressively increases the airflow resistance and thus decreases the flow of air through the filter arrangement.
After substantial saturation of the filter has occurred, it becomes impossible to establish a system differential pressure between the toilet and the waste water tank of sufficient strength to reliably convey the waste flow, due to the substantial pressure drop across the filter arrangement. As a result, there is the danger of blockage or plugging of the waste water collection line, which can ultimately lead to the failure of the entire toilet system. Since the conventional filter system cannot be cleaned during use, i.e. during the time it is installed in the toilet system, this progressive plugging or saturation of the filter arrangement cannot be corrected except for carrying out a substantial maintenance procedure of removing and replacing the filter arrangement, which involves substantial cost, effort and downtime of the aircraft.
Another problem is that some small waste particles, both solid and liquid, can permeate entirely through both filter stages, and thus be sucked into the exhaust air outlet line. There, the remaining waste particles will contaminate the mechanical components of the vacuum generator, which could lead to a malfunction or breakdown thereof, or are transported to the overboard outlet where the waste soils the outer skin of the aircraft fuselage.
A further disadvantage, as briefly mentioned above, is that the cleaning or maintenance of the filter system in conventional arrangements requires a substantial effort and expense. The waste water tank(s) with the conventional waste separator arranged thereon is(are) typically installed in the rear tail region behind the rearmost freight or cargo compartment in an aircraft, for example in an Airbus A340 aircraft. It is difficult to access the filter elements that must be cleaned or exchanged, and therefore it becomes necessary to carry out a complicated and time-consuming, and thus costly, disassembly, removal, reassembly and installation of these components at every scheduled maintenance interval that calls for inspection, cleaning, or replacement of the filter elements.
In view of the above, it is an object of the invention to provide a filter arrangement for a vacuum toilet system, especially for use in a commercial passenger transport aircraft, that has been improved so as to prevent a plugging or clogging and blockage of the filter element and therewith an impairment of the operability of the toilet system. It is a further object of the invention to provide such a filter arrangement having an increased operating lifetime in comparison to a conventional volume or bulk filter, and requiring a reduced effort for cleaning and maintenance procedures. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a filter arrangement for a vacuum toilet system, comprising a filter element for separating contaminants from a volume flow and particularly an airflow, arranged in a filter housing that is connected to the top of a waste water tank of the vacuum toilet system. The invention is directed to the filter element by itself, as well as the combination of the filter element with the filter housing and the waste water tank, or the filter arrangement in an overall vacuum toilet system.
Especially according to the invention, the filter element comprises a filter membrane of polytetrafluoroethylene (PTFE) that forms the surface of the filter element on the inlet or inflow side thereof, i.e. the side of the filter element facing the inflowing contaminated airflow. The housing has an outlet through which the cleaned or filtered volume flow is directed out of the filter arrangement, for example into an exhaust air line of the vacuum toilet system. The housing further forms a flow channel between the filter element and the housing wall, on the outlet or outflow side of the filter opposite the inlet side of which the surface is formed by the PTFE filter membrane. This flow channel acts as a plenum and leads and connects to the outlet. The housing has a drain or run-off opening through which contaminants separated from the airflow by the filter element can run back into the waste water tank. The PTFE filter membrane has a surface filtration effect, and a characteristic low adhesion so that contaminants do not adhere onto the filter membrane, but instead easily flow or fall downwardly from the filter element back into the waste water tank.
It is especially advantageous according to the invention, that a plugging or blocking of the filter arrangement can be effectively prevented, and thereby the operability and reliability of the vacuum toilet system cannot be impaired by a plugging or blocking of the filter. Thus, a reduction of the suction effect and ultimately a failure or breakdown of the entire toilet system due to a plugged filter is effectively prevented. Also, the effort and expense for the necessary maintenance measures as well as preventive maintenance inspections can be considerably reduced. Another advantage of the inventive arrangement is that solid and liquid contaminants are very effectively removed from the airflow, so that such contaminants will not be conveyed to and deposited on the outer skin of the aircraft or the components of the vacuum generator.
According to details of inventive embodiments, the filter element may further comprise a carrier material or substrate such as a supporting mesh or fleece of synthetic fibers, which supports and carries the PTFE filter membrane thereon. The PTFE filter membrane is preferably cylindrically configured, and may be folded or pleated in a fan-like manner into the form of a pleated filter so as to increase the filter surface area. The filter membrane may be supported by stabilizers or a support cage, and together therewith may form a unitary filter cartridge that can be easily installed in the filter housing and exchanged when necessary. The filter arrangement may further preferably comprise a cleaning or rinsing device, preferably embodied as a spray head including at least one liquid jet spray nozzle that directs a spray of a rinsing liquid onto the inlet side surface of the filter element, i.e. onto the PTFE filter membrane. Thereby, any solid contaminants adhering on the PTFE filter membrane are easily rinsed off so as to flow down into the waste water thank through the drain opening of the housing.